In February 1977, Chess 4.6, the only computer entry, surprised observers by winning the 84th Minnesota Open against competitors just under Master level.
It achieved a USCF rating close to or at Expert, higher than previous programs' Class C or D, by winning five games and losing none.
[1] In 1978, the improved Chess 4.7—which had by now achieved a 2030 rating after 31 tournament games[5]—played against David Levy who, in 1968 had wagered that he would not be beaten by a computer within ten years.
Whereas Chess 4.7 had beaten Levy under blitz conditions, the bet involved forty moves over a two-hour period, the computer's choices being relayed by telephone from Minnesota to the board.
[9] Levy wrote, "I had proved that my 1968 assessment had been correct, but on the other hand my opponent in this match was very, very much stronger than I had thought possible when I started the bet.
It won the 10th ACM North American Computer Chess Championship tournament in Detroit and played at the expert level (2100).
David Slate, with William Blanchard of Vogelback Computing Center at Northwestern University, later wrote a new program in Fortran, originally dubbed "Chess 5.0", but later renamed Nuchess.